At some point most children will have a fear of monsters. It might be a fear of the dark or that there's a monster in their closet or under their bed.
As a parent it's tempting to dismiss your child's fear by saying "There's no such thing as monsters." That approach usually doesn't alleviate their fear. Young children have magical thinking which gets fused with their perception of reality. To them monsters are very real.
Here are some strategies to help manage the fear.
Monster Spray: Buy an inexpensive can of air freshener. A lavender scent would be a good choice as it has a calming effect. Put a label on the can that says, "GO AWAY MONSTER!” Spray it in your child's room as part of their bedtime routine.
A fear of monsters will probably make an appearance in your home. Approach that fear calmly and reassuringly and your child will feel safe and secure.